The present invention relates to a timing signal generating apparatus for a rotating device, and more particularly to a timing signal generating device for a rotating device for obtaining, by way of example, a timing signal for controlling the fuel injection timing etc. of a fuel injection pump.
Generally, in the case where electrical control is performed with respect to a rotating device such as an electric motor, internal combustion engine or the like, it is frequently necessary to obtain a timing signal which accurately indicates the desired rotation timing of the rotating device. Such a timing signal becomes necessary in the case where the injection timing of fuel is electronically controlled so as to obtain an optimum injection timing corresponding to the operating condition of the engine. In order to obtain such a timing signal in a conventional internal combustion engine, there is generally used a pulse generator for generating a pulse every time the rotating shaft or the like of the engine rotates a predetermined angle, and the rotation angle at each instant is detected by counting the number of pulses output from the pulse generator (Japanese Patent Public Disclosure Nos. Sho 57-124208 and Sho 58-86407).
According to the conventional construction, it is necessary to increase the density of pulse generation from the pulse generator in order to increase the accuracy of the timing signal, and in order to do this, the number of cogs or slits of the pulser of the pulse generator must be increased. However, there is a limit to the number of cogs or slits that can be provided from the point of view of mechanical construction. Furthermore, from the fact that increasing the number of cogs or slits raises the manufacturing cost, there is also an economic limit on increasing the density of pulse generation. Because of this, there has been proposed a device in which the timing between two successive cogs or slits is determined by interpolation or by multiplying the frequency of the output pulse signal. However, no prior art device is able to provide the desired timing signal with high accuracy in the case where the engine speed suddenly changes, so that highly accurate timing control has not been possible.